The invention is directed to ceramic products made from waste glass; raw batch formulations for making ceramic products from waste glass; and a method for making ceramic products from waste glass. The invention provides a low-cost method of manufacturing ceramic products from waste glass with the addition of a solid organic binder, without the use of water or any other liquid solvent. This method is especially useful for processing water-sensitive glass compositions into ceramic products, but water-insensitive glass compositions can also be used. A wide variety of ceramic products can be manufactured by the invention. Examples are provided where the invention is used to make ceramic tile from different types of recycled waste glass.
The invention also addresses two current problems: energy usage by the ceramic industry needs to be reduced; and new recycled-glass products are needed. The ceramic industry consumes large amounts of energy, especially during the firing process. Firing temperatures greater than 1200° C. (2200° F.) are required to sinter typical ceramic raw materials into dense products. Modifications of the raw material formulations have led to reductions in firing temperatures, but the improvements are limited because of the types of raw materials used. Most traditional ceramic products, such as tile and brick, consist mainly of clay-based raw materials, which inherently require high firing temperatures. Other ceramic manufacturing steps, such as the drying processes, are also very energy intensive. Energy costs are a major portion of the total manufacturing costs, and thus new methods to reduce the amount of energy required will be a great benefit to the ceramic industry.
New products utilizing recycled waste glass are needed to further promote glass recycling, because only a limited amount of glass can be remelted to make new containers (currently the primary use of recycled glass). New products are especially needed that are less sensitive to contaminants in the glass, and that can be made from green or mixed-color container glass waste. Research has been conducted and products developed using recycled glass as a ceramic raw material. However, processing problems have limited the developments, so that only a negligible amount of waste glass is currently utilized (excluding remelting to form new glass products). These problems occur because of inherent chemical and processing incompatibilities with traditional ceramic raw materials and manufacturing methods. These incompatibilities have greatly hampered the development of ceramic products from waste glass.
U.S. Pat. No. 6,340,650 reviews previous waste glass processing problems, and provides a new method to eliminate these problems by avoiding the use of water and clay in the processing. This method includes the addition of an organic binder to bond the waste glass particles together in the forming process. The organic binder is initially either in either a liquid or solid state. If a solid organic binder is used, then the binder is dissolved in a nonaqueous liquid. This method eliminates previous problems, however there are still some disadvantages. The present invention eliminates these disadvantages, as discussed in the following paragraphs.
To be effective an organic binder needs to be in liquid form, so that the waste glass particles can be wetted and coated by the organic binder. A single phase organic binder at room temperature (˜20° C.) is in either a liquid or solid state. If an organic binder is in a liquid state, then the ceramic particles can be directly mixed with the binder to coat the particles. The mixture can then be formed into the desired article, but the green strength of the article will be low compared to if the binder is in a solid state. The green strength refers to the strength of the unfired green article produced after the forming step. The green strength needs to be high enough so that the articles can be transferred from the forming step to the firing step without breakage. In addition, the level of green strength required increases as the size of the article increases.
If the organic binder is in a solid state, then the binder can be dissolved in specific liquids, mixed with the waste glass particles, and then dried to remove the liquid to produce waste glass particles coated with the organic binder. Water is commonly used as the liquid. For water-sensitive ceramic raw materials, water can be replaced with nonaqueous liquids, such as alcohols. However, processing with nonaqueous liquids increases the cost and complexity of manufacturing, and can add environmental problems.
The present invention involves a new method of coating waste glass powder with a solid organic binder, which improves the green strength compared to when a liquid binder is used. The invention also eliminates the need for water or any other liquid solvent. In the invention the binder is initially a solid, which is then melted to form a liquid, coated on the glass powder, and cooled to solidify the binder to form a solid-binder-coated-glass mixture. The mixture is then formed into a green article, and fired into a high-quality ceramic product.
The invention can be used to produce an impervious ceramic microstructure with only a small amount of porosity. Impervious refers to ceramic products with very low water absorptions of less than 0.5%. An impervious ceramic microstructure with a small amount of porosity is critical to achieve high-quality properties. Ceramic products can be produced by the invention with a wide range of colors with smooth glossy glaze-like surfaces. The surface texture and other fired properties can also be adjusted by the addition of fillers, and/or by partial crystallization of the glass. The invention conserves energy and natural resources compared to traditional ceramic processing methods.